Breech seal for air gun

ABSTRACT

A barrel break air gun includes a pair of opposed, generally planar faces defining a narrow gap between the breech and the barrel. The barrel face includes a circular groove concentric with the barrel bore that receives an annular seal, and a recessed annular land defined between the circular groove and the barrel bore. The annular seal may be either an o-ring nominally disposed within the circular groove, or an annular urethane washer that is slightly radially-compressed when placed into the circular groove such that the inner diameter of the washer projects slightly away from the barrel face prior to closing the barrel breech. In one embodiment featuring the annular washer, the washer&#39;s internal diameter is slightly smaller than the maximum skirt dimension of an air gun pellet, such that the pellet&#39;s skirt is retained by the washer upon closing the barrel breech.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit if U.S. Provisional Patent Application Ser. No. 61/160,702, filed on Mar. 16, 2009, the disclosure of which is hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to air guns and, particularly, to a barrel and breech seals for such air guns.

BACKGROUND OF THE INVENTION

Known barrel break air guns fire projectiles using compressed air that is delivered to a gas transfer port disposed in the gun breech, immediately rearward of a projectile, such as a pellet, disposed in the barrel proximate to the breech. The barrel is pivotally connected to the breech, such that the barrel can be “broken” to expose the rearward extent of the barrel's bore in order to receive the pellet, whereupon the pellet is retained in the rearward extent of the barrels' bore by static friction until firing.

The opposed generally planar faces of the breech and the barrel are typically sealed by an o-ring disposed in a concentric groove machined on one of the faces, such as the rearward face of the barrel. Upon pivoting the barrel into a closed position, in general alignment with the axis of the gas transfer port of the breech, the o-ring is slightly axially compressed between the opposed breech and the barrel faces to achieve an air-tight seal between the breech and the barrel. Thus, when the air gun is fired, for example, by triggering the release of a spring-driven piston within a compression tube defined within the breech, or other suitable source of compressed gas, a volume of highly-compressed gas is directed through the gas transfer port and into the barrel. The effectiveness of the breech seal plays a significant role in the efficiency of the air blast that is delivered into the barrel bore, which, in turn, determines the air gun's muzzle velocity and firing performance.

In order to achieve a greater muzzle velocity without increased air loss through the breech seal, the prior art has sought to generate an increase in the gas flow rate through the gas transfer port by increasing the port's cross-sectional area, with the correlative effect of reducing the peak pressure achieved behind the projectile seated in the barrel bore to reduce air losses through the breech seal. This approach has been known to slightly improve muzzle velocities over a stock breech. However, the use of an increased port cross-sectional area often generates increased physical shock as the piston slams into the end of the compression bore due to a reduction in piston back-pressure, such that the air gun is more difficult to shoot accurately, and with reduced smoothness. Further, an increased port cross-sectional area appears to more gradually ramp up the pressure achieved behind the seated projectile, such that the static friction retaining the projectile in the barrel bore proximate the breech is overcome well before peak pressure is achieved, thereby further mitigating the performance increase that might otherwise be achieved from an increased gas flow rate.

SUMMARY OF THE INVENTION

An air gun includes a receiver. The receiver includes a breech face, and also defines a gas port configured for exhausting a compressed gas therethrough. The air gun further includes a barrel defining a bore extending along a longitudinal axis of the barrel. The barrel includes a barrel face disposed opposite the breech face. The bore is in fluid communication with the gas port for receiving the compressed gas. The barrel defines a circular groove disposed concentrically about and radially offset from the bore. The circular groove is recessed a depth from the barrel face. A seal is at least partially disposed within the circular groove. The seal is in sealing engagement with the breech face of the receiver for sealing the bore and the gas port between the barrel and the receiver. The barrel further includes an annular land disposed adjacent and concentrically about the bore, between the circular groove and the bore. The annular land is recessed from the barrel face a depth less than the recessed depth of the circular groove.

In another aspect of the invention, an air gun is provided. The air gun includes a receiver having a breech face. The receiver further defines a gas port configured for exhausting a compressed gas therethrough. The air gun further includes a barrel defining a bore extending along a longitudinal axis of the barrel. The barrel includes a barrel face disposed opposite the breech face. The bore is in fluid communication with the gas port for receiving the compressed gas. The barrel defines a counterbore disposed concentrically about and adjacent the bore of the barrel. The air gun further includes a seal at least partially disposed within the circular counterbore. The seal is in sealing engagement with the breech face of the receiver for sealing the bore and the gas port between the barrel and the receiver. The seal includes a cylindrical body. The cylindrical body extends along the longitudinal axis. The seal includes a second flange that is disposed at a second end of the cylindrical body, and extends radially inward from the cylindrical body to a radial inner surface. The radial inner surface includes a diameter less than a diameter of the bore.

In another aspect of the invention, an air gun is provided. The air gun includes a receiver. The receiver defines a gas port that is configured for exhausting a compressed gas therethrough. The air gun further includes a barrel. The barrel defines a bore extending along a longitudinal axis of the barrel. The barrel includes a barrel face. The bore is in fluid communication with the gas port for receiving the compressed gas. The air gun further includes a seal. The seal is in sealing engagement with the barrel face and the receiver. The seal seals the bore and the gas port. The seal also defines an interior diameter that is less than a diameter of a projectile. The interior diameter engages at least a portion of the projectile for retaining the projectile in place until fired.

The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged, partial view in longitudinal cross-section of a single-shot break barrel air gun incorporating a first exemplary breech seal in accordance with an aspect of the invention.

FIG. 2 is an enlarged cross-sectional view of the first exemplary breech seal, with the breech closed.

FIG. 3 is an enlarged cross-sectional view of a second exemplary breech seal, in accordance with another aspect of the invention.

FIG. 4 is an enlarged cross-sectional view of a modified washer seal, prior to installation in the barrel face.

FIG. 5 is an enlarged cross-sectional view of a third exemplary breech seal incorporating the modified washer seal of FIG. 4, in accordance with another aspect of the invention.

FIG. 6 is an enlarged cross-sectional view of an alternative embodiment of a barrel incorporating the third exemplary breech seal shown in FIG. 5.

FIG. 7 is an enlarged cross-sectional view of a fourth exemplary breech seal, in accordance with yet another aspect of the invention.

FIG. 8 is an enlarged cross-sectional view of a fifth exemplary breech seal in an alternative embodiment of the air gun.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, a break barrel air gun 10 includes a receiver 12 defining an internal compression chamber 14 for generating a quantity of compressed gas upon powered translation of a piston 16 within the chamber 14. The piston 16 may be powered by a coil spring, a gas spring, compressed gas, or some other power source suitable for the air gun 10. A barrel 18 is pivotally mounted on an end of the receiver 12, such that a barrel face 20 defined on a rearward end of the barrel 18 is pivoted away from a breech face 22, which is defined on a forward rend of the receiver 12, to provide access to a breech 24, whereby a pellet 26 can be loaded into the breech 24. When closed to place the barrel face 20 in general parallel-spaced opposition with the breech face 22, a barrel bore 28, which extends along a longitudinal axis 33, is placed in general axial alignment with a gas transfer port 30 that is defined in the breech face 22, by which compressed air is delivered from the compression chamber 14 to the barrel bore 28 upon firing. Alternatively, as is shown in FIG. 8, the gas transfer port 30 may be disposed perpendicularly relative to the longitudinal axis 33 of the barrel bore 28, and may not extend through the breech face 22.

As best seen in FIG. 2, the air gun 10 includes a first exemplary breech seal 32 in accordance with the invention. Specifically, the barrel face 20 includes a circular groove 32 that is generally concentric with and radially offset from the barrel bore 28. The circular groove 34 is adapted to receive a seal 32, which is at least partially disposed within the circular groove 32. The seal 32 is in sealing engagement with the breech face 22 of the receiver for sealing the barrel bore 28 and the gas port 30 between the barrel 18 and the receiver 12. As shown in FIG. 2, the seal 32 may include an o-ring seal 36. A recessed annular land 38 is also defined on the barrel face 20 between the circular groove 34 and the barrel bore 28. The annular land 38 is disposed adjacent and concentrically about the barrel bore 28. The maximum depth of the annular land 38, relative to the barrel face 20, is less than the nominal depth of the circular groove 34 relative to the barrel face 20. In other words, the annular land 38 is recessed from the barrel face 20 a depth that is less than the depth the circular groove 34 is recessed from the barrel face 20. While the annular land 38 may be formed generally orthogonal to the bore axis, in the first breech seal 32, the annular land is provided with a radial draft angle by which the land depth increases slightly with increasing distance from the bore axis.

The first breech seal 32 is believed to provide an expansion area that temporarily receives the high forces of compressed air flow through the gas transfer port 30. These forces are allowed to divert dynamically radially away from the pellet 26 seated in the barrel bore 28 and are believed to improve the effectiveness of the o-ring seal 36 by radially elastically deforming the o-ring seal 36 and, hence, increasing the seal's axial compression between the opposed barrel face 20 and breech face 22. Further, the first breech seal 32 is believed to dynamically absorb a portion of these forces, thereby modulating piston back pressure to significantly reduce the likelihood that the piston 16 will slam into the end of the compression chamber 14, and increasing air gun smoothness. By way of example, in a constructed embodiment of the first air gun 10, the use of the stepped breech seal pocket achieved improved muzzle velocities of as much as thirteen percent, depending on pellet caliber.

Referring to FIG. 3, a second exemplary breech seal 40 in accordance with another aspect of the invention includes the circular groove 34 and annular land 38 in the barrel face 20 as in the first breech seal of FIGS. 1 and 2. The second breech seal 40 includes an annular washer 42 having outer diameter 44 that is greater than an outer diameter of the circular groove 34. In other words, the annular washer 42 is sized such that the annular washer 42 is slightly radially-compressed when placed into the circular groove 34, such that the radially-innermost portion of the annular washer 42 projects slightly away from the barrel face 20 prior to closing the breech 24. Additionally, the annular washer 42 includes a thickness measured along the longitudinal axis 33 that is greater than the difference between the recessed depth of the circular groove 34 and the recessed depth of the annular land 38 relative to the barrel face 20. Having the thickness of the washer 42 greater than the difference between the recessed depths relative to the barrel face 20 ensures that the washer 42 extends beyond the barrel face 20. While the invention contemplates use of any suitable seal material, the seal may advantageously be formed from an elastomer such as a urethane material, or of rubber, preferably having a durometer of at least about 40, and preferably having a durometer less than about 90. The annular washer may advantageously be stamped or cut from sheet stock, molded, or cast depending upon material choice.

In accordance with another aspect of the invention, the washer's radial inner surface 46 includes diameter that is less than a diameter of the barrel bore 28, which is slightly smaller than the maximum skirt dimension of the pellet 26, such that the pellet skirt 48 is retained by the washer's radially inner surface 46 upon closing the breech 24. In accordance with yet another aspect of the invention, the washer's radially inner surface 46 is provided with a contour or other surface feature to customize initial pellet retention upon closing the breech, and/or the pellet breakaway force. Thus, in a constructed embodiment, the radially inner surface 46 retains the pellet skirt 48 slightly closer to the barrel side of the washer's thickness, to improve pellet release circumferential contact between the washer and the pellet skirt upon closing of the breech, it will be appreciated that the invention contemplates other configurations for the washer's central bore, for example, by which to achieve three-point contact with the pellet's skirt. The washer's central bore may alternatively be provided with surface features, such as ribs or a threadform, to achieve a repeatable breakaway force notwithstanding nominal variation in skirt dimensions.

Referring to FIGS. 4 and 5, a third exemplary breech seal 50 in accordance with another aspect of the invention likewise includes the circular groove 34 and annular land 38 in the barrel face 20 as in the first and second breech seals 32, 40. In the third breech seal 50, the annular washer 52 is formed with a generally cylindrical body 54 and a radially-inward flange 56 which projects slightly axially away from the cylindrical body 54 to thereby project slightly toward the opposed breech face 22 when the washer's cylindrical body 54 is received in the barrel face's circular groove 34. The cylindrical body 54 includes a length along the longitudinal axis 33 that is greater than the depth of the circular groove 34 relative to the barrel face 20. The flange 56 includes a thickness measured along the longitudinal axis 33 that is greater than the depth of the annular land 38 relative to the barrel face 20. The flange 56 defines a radially inner surface 58 having a diameter that is less than the diameter of the barrel bore 28. Upon closure of the breech 24, the washer's radial flange 56 flexes axially to improve the quality of the seal, while also radially contracting slightly to more securely retain the pellet skirt 48. As in the second breech seal 40, the radially inner surface 58 of the washer's radial flange 56 is provided with a suitable contour and/or surface feature to provide a consistent pellet retention force, such as a threadform (not shown), and to nominally position the pellet skirt at a desired depth relative to the barrel face 20.

Referring to FIG. 6, the third breech seal 50 is shown in with an alternative embodiment of the barrel 100. The alternative embodiment of the barrel 100 includes an outer portion 102 and an inner portion 104. The outer portion 104 defines the annular groove 34, and includes a nut 106 disposed within the annular groove 34 and rotationally fixed about the longitudinal axis 33. The inner portion 104 includes a threaded end 108, and is slideably disposed within the outer portion 102. The threaded end 108 is in threaded engagement with the nut 106 to secure the inner portion 104 relative to the outer portion 102. The inner portion 102 defines the bore 28. Accordingly, in the configuration shown in FIG. 6, the inner portion 104 of the barrel 18 may be replaced, such as for example, to change the caliber of the air gun. The threaded end 108 of the inner portion 104 cooperates with the outer portion 102 to define the circular groove 34. As such, the third breech seal 50 is disposed within the circular groove 34, between the outer portion 102 and the inner portion 104 of the barrel 100. As shown in FIG. 5, the annular washer 52 is formed with a generally cylindrical body 54 and a radially-inward flange 56 which projects slightly axially away from the cylindrical body 54 to thereby project slightly toward the opposed breech face 22 when the washer's cylindrical body 54 is received in the barrel face's circular groove 34. The cylindrical body 54 includes a length along the longitudinal axis 33 that is greater than the depth of the circular groove 34 relative to the barrel face 20. The flange 56 includes a thickness measured along the longitudinal axis 33 that is greater than the depth of the annular land 38 relative to the barrel face 20. The flange 56 defines a radially inner surface 58 having a diameter that is less than the diameter of the barrel bore 28. Upon closure of the breech 24, the washer's radial flange 56 flexes axially to improve the quality of the seal, while also radially contracting slightly to more securely retain the pellet skirt 48. As in the second breech seal 40, the radially inner surface 58 of the washer's radial flange 56 is provided with a suitable contour and/or surface feature to provide a consistent pellet retention force, such as a threadform (not shown), and to nominally position the pellet skirt at a desired depth relative to the barrel face 20.

Referring to FIG. 7, a fourth exemplary breech seal 60 in accordance with another aspect of the invention includes a counterbore 62 defined in the barrel face 20. The counterbore 62 is disposed concentrically about and adjacent the barrel bore 28. It will be appreciated that a circular groove and annular land as in the first, second, and third breech seals 32, 40, 50 may also be used in place of the simple counterbore 62 as seen in FIG. 7. The fourth breech seal 60 includes an annular washer 64 that includes a generally cylindrical body 66 that extends along the longitudinal axis 33, a radially-outward first flange 68 on one end of the cylindrical body 66 that overlies at least a portion of the barrel face 20 concentric with the counterbore 62, and a radially-inward second flange 70 on the other end of the cylindrical body 66 that projects radially inwardly to mechanically capture the pellet skirt 48. The first flange 68 is disposed between the barrel face 20 and the breech face 22. The second flange 70 has an inner diameter that is less than the diameter of the barrel bore 28, which is slightly less than the nominal skirt diameter of the pellet 26, such that the pellet skirt 48 is elastically retained within the washer's second flange 70 prior to firing. As in the second and third breech seals 40, 50, the inner surface 72 of the washer's second flange 70 preferably includes a contour to help retain the pellet skirt at a predetermined depth relative to the barrel face 20. The counter bore 62 extends a depth along the longitudinal axis 33 relative to the barrel face 20, and the second flange 70 includes a thickness along the longitudinal axis 33 relative to the barrel face that is less than the depth of the counterbore 62. Accordingly, the depth of the counterbore 62 and the second flange 70 may be sized to substantially equal a length of the pellet 26, so as to engage both a body of the pellet and the pellet skirt 48 (as shown), or alternatively, may be sized so as to only engage the pellet skirt 48.

Referring to FIG. 8, a fifth alternative embodiment of the breech seal is shown generally at 120. The fifth breech seal 120 is shown in an alternative embodiment of the air gun 122. More specifically, the fifth breech seal 120 is shown in an inline bolt action air gun. The inline bolt action air gun 122 includes a loading mechanism 124 for loading the projectile, i.e., the pellet 26. The loading mechanism 124 includes an inline bolt 126, which moves axially along and inline with the longitudinal axis 33 to move the pellet 26 into position within the breech of the barrel 18. The air gun 122 includes a receiver 128, which defines a gas port 30. The gas port 30 is configured for exhausting a compressed gas therethrough, into a firing chamber disposed behind the pellet 26, between the pellet 26 and a barrel face 130 of the loading mechanism 124.

The barrel 18 defines a bore 28, which extends along the longitudinal axis 33 of the barrel 18. The bore 28 is in fluid communication with the gas port 30 for receiving the compressed gas. The fifth breech seal 120 is in sealing engagement with the barrel face 130 and the receiver 128 for sealing the bore 28 and the gas port 30. The fifth breach seal 120 defines an interior diameter 132 that is less than an outer diameter 134 of the pellet 26. The smaller interior diameter 132 of the fifth breech seal 120 engages at least a portion of the pellet 26, and retains the pellet 26 in place until fired. Preferably, the fifth breech seal 120 includes a durometer greater than or equal to 40 and less than or equal to 90, so as to be able to flex as the pellet 26 is loaded into a secured position by the bolt 126 of the loading mechanism 124, while still maintaining sufficient rigidity to secure the pellet 26 in place until gas pressure behind the pellet 26 is sufficient to fire the pellet 26.

As shown, the barrel may define a counterbore 62 disposed concentrically about and adjacent the bore of the barrel. The fifth breech seal 120 is at least partially disposed within the counterbore 62. However, it should be appreciated that the air gun 122 need not include the counterbore 62, and the fifth breech seal 120 may be disposed in abutting engagement with, i.e., immediately adjacent to, the breech face 22 of the barrel 18. As described above, the loading mechanism 124 is configured for urging the pellet 26 into a secured position within the seal 120, in preparation for firing. When the loading mechanism 124 is positioned in a firing position, the fifth breech seal 120 is configured for sealing against the barrel face 130 of the loading mechanism 124, i.e., against an end of the bolt 126 facing the pellet 26. The seal may defines a port 138 adjacent and in fluid communication with the gas transfer port 30, through which the compressed gas flows.

In accordance with yet another aspect of the invention, in each of the second, third, fourth and fifth breech seals 40, 50, 62, 120 through suitable selection of the washer's/washer flange's internal diameter and contour, and the washer material's durometer, the pellet breakaway force can be set such that the piston 16 finishes its movement within the compression chamber 14 and comes to a complete stop at roughly the same time that the pellet 26 breaks from the washer. Thus, these breech seals 40, 50, 62, 120 advantageously permit the use of larger compression springs and pistons with greater mass, without generating unwanted piston slam. Further, the resulting improved seal quality permits use of larger caliber projectiles with a given breech, thereby lowering air gun cost and weight by allowing use of a smaller frame.

While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims. 

1. An air gun comprising: a receiver having a breech face and defining a gas port configured for exhausting a compressed gas therethrough; a barrel defining a bore extending along a longitudinal axis of said barrel and including a barrel face disposed opposite said breech face, wherein said bore is in fluid communication with said gas port for receiving the compressed gas; said barrel defining a circular groove disposed concentrically about and radially offset from said bore and recessed a depth from said barrel face; a seal at least partially disposed within said circular groove and in sealing engagement with said breech face of said receiver for sealing said bore and said gas port between said barrel and said receiver; and an annular land disposed adjacent and concentrically about said bore between said circular groove and said bore and recessed from said barrel face a depth less than said recessed depth of said circular groove.
 2. An air gun as set forth in claim 1 wherein said seal includes a durometer greater than or equal to 40 and less than or equal to
 90. 3. An air gun as set forth in claim 2 wherein said seal includes an o-ring seal.
 4. An air gun as set forth in claim 2 wherein said seal includes a washer.
 5. An air gun as set forth in claim 4 wherein said washer includes a thickness greater than a difference between said depth of said circular groove relative to said barrel face and said depth of said annular land relative to said barrel face.
 6. An air gun as set forth in claim 5 wherein said washer defines an outer diameter greater than an outer diameter of said circular groove.
 7. An air gun as set forth in claim 6 wherein said washer defines a radially inner surface having a diameter that is less than a diameter of said bore of said barrel.
 8. An air gun as set forth in claim 7 wherein said radial inner surface of said washer includes at least one surface feature for contacting a pellet disposed in said bore and configured for providing a consistent breakaway force between the pellet and said bore.
 9. An air gun as set forth in claim 4 wherein said washer includes a cylindrical body disposed within said circular groove and a flange extending radially inward from said body adjacent said annular land.
 10. An air gun as set forth in claim 9 wherein said body includes a length along said longitudinal axis that is greater than said depth of said circular groove relative to said barrel face.
 11. An air gun as set forth in claim 10 wherein said flange includes at thickness greater than said depth of said annular land relative to said barrel face.
 12. An air gun as set forth in claim 9 wherein said flange defines a radially inner surface having a diameter that is less than a diameter of said bore of said barrel.
 13. An air gun as set forth in claim 12 wherein said radial inner surface of said flange includes at least one surface feature for contacting a pellet disposed in said bore and configured for providing a consistent breakaway force between the pellet and said bore.
 14. An air gun comprising: a receiver having a breech face defining a gas port configured for exhausting a compressed gas therethrough; a barrel defining a bore extending along a longitudinal axis of said barrel and including a barrel face disposed opposite said breech face, wherein said bore is in fluid communication with said gas port for receiving the compressed gas; said barrel defining a counterbore disposed concentrically about and adjacent said bore of said barrel; and a seal at least partially disposed within said circular counterbore and in sealing engagement with said breech face of said receiver for sealing said bore and said gas port between said barrel and said receiver; wherein said seal includes a cylindrical body extending along said longitudinal axis and a second flange disposed at a second end of said cylindrical body and extending radially inward from said cylindrical body to a radial inner surface having a diameter less than a diameter of said bore.
 15. An air gun as set forth in claim 14 wherein said counter bore extends a depth along said longitudinal axis relative to said barrel face and said second flange includes a thickness along said longitudinal axis relative to said barrel face that is less than said depth of said counterbore.
 16. An air gun as set forth in claim 15 wherein said radial inner surface of said second flange includes at least one surface feature for contacting a pellet disposed in said bore and configured for providing a consistent breakaway force between the pellet and said bore.
 17. An air gun as set forth in claim 16 wherein said seal includes a first flange disposed at a first end of said cylindrical body between said barrel face and said breech face, and extending radially outward from said cylindrical body.
 18. An air gun as set forth in claim 17 wherein said seal includes a durometer greater than or equal to 40 and less than or equal to
 90. 19. An air gun comprising: a receiver defining a gas port configured for exhausting a compressed gas therethrough; a barrel defining a bore extending along a longitudinal axis of said barrel and including a barrel face, wherein said bore is in fluid communication with said gas port for receiving the compressed gas; and a seal in sealing engagement with said barrel face and said receiver for sealing said bore and said gas port, and defining an interior diameter less than a diameter of a projectile for engaging at least a portion of the projectile and retaining the projectile in place until fired.
 20. An air gun as set forth in claim 19 wherein said seal includes a durometer greater than or equal to 40 and less than or equal to
 90. 21. An air gun as set forth in claim 20 wherein said barrel defines a counterbore disposed concentrically about and adjacent said bore of said barrel, with said seal at least partially disposed within said counterbore.
 22. An air gun as set forth in claim 20 further comprising loading mechanism configured for urging the projectile into a secured position within said seal.
 23. An air gun as set forth in claim 22 wherein the loading mechanism is disposed inline with said longitudinal axis, with said seal configured for sealing against a barrel face of said loading mechanism.
 24. An air gun as set forth in claim 23 wherein said seal defines a port adjacent and in fluid communication with said gas transfer port. 